1. Field of the Invention
This invention relates to a zoom lens barrel wherein zooming is effected by rectilinear movement of an operating ring and focusing is effected by rotation of the operating ring.
2. Description of the Prior Art
In a zoom lens barrel of this type, a single pin is projectedly provided on a magnification changing lens frame member holding a magnification changing lens and this pin is moved in the direction of the optical axis by rectilinear movement of the operating ring, thereby accomplishing zooming. However, if the length of the magnification changing lens frame member which is driven by the single pin is short, the magnification changing lens frame member becomes inclined during the movement thereof and cannot slide smoothly. This has led to the disadvantage that the length of the magnification changing lens frame member has necessarily been large and consequently the length of the entire lens barrel has also been large. On the other hand, in a zoom lens barrel of the type in which zooming operation is accomplished by rotation of the operating ring about the optical axis, three pins are projectedly provided on the magnification changing lens frame member equidistantly along the circumferential direction thereof, these three pins are inserted into three inclined cam grooves formed in a cam ring, and this cam ring is rotated by rotation of the operating ring to thereby move the magnification changing lens frame member in the direction of the optical axis. In the zoom lens barrel of this type, the three pins are held by the cam ring and, therefore, the magnification changing lens frame member need not be made long in the direction of the optical axis. However, if there is any back-lash between the pins and the width of the inclined grooves, a back-lash greater than said back-lash will occur in the direction of the optical axis because of the inclination of the inclined grooves, so that the magnification changing lens cannot be held in a plane perpendicular to the optical axis. Thus, an adverse effect will occur to the lens performance.